1. Field of the Invention
The present invention generally relates to a lithium secondary battery, and more specifically, to a lithium secondary battery configured to divide electrolytes formed between electrodes of the lithium secondary battery into a plurality of regions to increase energy density, prevent degradation of stability due to growth of dendrite and improve cycle characteristics.
2. Description of the Related Art
Recently, interest on energy storage technology has been increased. In the energy storage technology, efforts of research and development of the energy storage technology have been specified as its application fields have been expanded into batteries for electric automobiles as well as portable electronic equipment
An electric chemical device has been most noted in this aspect, and development of secondary batteries that can be charged and discharged has been focused. Due to development of smaller and lighter electric apparatus, smaller and lighter batteries used as a power source have been largely requested. As a result, in order to improve capacity density and non-energy of batteries, design of new electrodes and batteries has been recently researched and developed.
FIG. 1 is a diagram illustrating a structure illustrating a conventional lithium metal battery.
In the conventional lithium metal battery, an anode 1 and a cathode 2 are separated with polymer electrolytes 3 that enable movement of lithium ions so as to prevent a short of the electrodes 1 and 2. Also, in the conventional lithium metal battery, a separating film 4 is comprised between the anode 1 and the cathode 2 for smooth performance of electric generation reaction.
In the above-described conventional lithium metal battery, its energy density is about 3800 mAh/g. However, as charging is repeated in the lithium metal battery of FIG. 1, a dendrite 6 is generated as shown in FIG. 2 and stability is degraded due to reactivity between the dendrite 6 and electrolytes. For example, when lithium ions move continuously from the anode to the cathode while lithium is geometrically filled in an empty space of the crystal structure of the cathode 2 in excessive charging, the dendrite 6 is grown from the surface of the cathode 2 as shown in FIG. 2. If the dendrite 6 is continuously grown, it may perforate a separating film 4 and contact with the anode 1. In this case, the battery emits large energy explosively to cause fire. This phenomenon can be serious as the energy density of the lithium metal battery increases.
In order to overcome the above-described phenomenon, instead of metal lithium or its alloys, carbon materials using an absorption-emission process of lithium ions and matrix materials including conductive polymers have been recently developed for the cathode 2.
However, since a lithium ions secondary battery that uses carbon materials as the cathode does not employ lithium metals as the cathode, reaction between active lithium and electrolytes is not generated. Although the lithium ions secondary battery prevents a short between the electrodes 1 and 2 by dendrite, the lithium ions are doped between carbon layers so that capacity per gram is reduced corresponding to the amount of carbon. That is, when carbon materials is used as the cathode, the stability can be strengthened, but the theoretical energy density is remarkably decreased to about 370 mAh/g compared with the case the lithium metal is used.
Recently organic liquid electrolytes have been used as electrolytes. However, the liquid electrolytes may be leaked out of parts. Although a lithium polymer battery that uses solid electrolytes has been developed in order to prevent leakage of electrolytes, this lithium polymer battery does not solve the problem of dendrite while increasing of the energy density.